Qatari troops are part of the Gulf forces deployed to Bahrain to put down Shiite-led protests against the Sunni dynasty there, said a Qatari military official.

"The duty of the Qatari force participating in the Peninsula Shield force is to contribute in restoring order and security" in Bahrain, Qatar news agency QNA quoted Colonel Abdullah Al-Hajri as saying late Thursday.

This is the first official confirmation of Qatar's contribution to Gulf troops in Bahrain.

"As a Qatari force we are receiving our orders from the head of the joint Peninsula Shield Force. There are no Qatari forces outside the Peninsula Shield" in Bahrain, Hajri said.

Earlier this week, more than 1,000 Saudi troops and around 500 Emirati troops entered the strategic Gulf kingdom, home to the US Fifth Fleet.

The move was met with strong criticism from Iran and followed by Tehran and Manama withdrawing their respective ambassadors.

US Secretary of State Hillary Clinton called the situation in Bahrain "alarming" after about 16 people were killed in violence there and criticised Washington's Gulf state allies for heading down "the wrong track" of military intervention.

UN Secretary General Ban Ki-moon also warned Bahrain that its crackdown on anti-government protesters might be breaking international law after his human rights chief spoke of "shocking and illegal" abuses.

Dissidents had been rounded up at gunpoint in midnight raids and armed police stood outside Manama's main hospital on Thursday, amid reports the authorities were beating doctors and denying treatment to the wounded.

Opposition protesters are demanding far-reaching democratic reform in the mainly Shiite country which has been ruled by a Sunni Muslim dynasty for more than 200 years.

King Hamad has offered dialogue and a new, empowered parliament among other reforms but the opposition refuses to sit down to talks before the government resigns.

The king on Tuesday declared a three-month state of emergency in the country after the Gulf troops arrived.